The present invention relates to a disk playback apparatus for playing back a disk such as a video disk and a digital audio disk.
So far, when information such as music recorded on a CD (compact disk) as a digital audio disk is read, the spindle motor for driving the disk has been controlled, for example, as disclosed in Japanese laid-open Patent publication No. 59-77673 (G11B19/24). More specifically, since control by the CLV system, in which the CD is revolved at a constant linear velocity, is executed in the reading of the CD, the linear velocity of the CD is required to be constant throughout the reading of the CD from its inside to its outside. To achieve this, the number of revolutions of the disk is changed approximately from 600 rpm when the inside is read to 200 rpm when the outside is read.
Further, in order to keep the linear velocity constant even during a short period that corresponds to one to several revolutions, while adapting it to the eccentricity factor, the spindle motor has been arranged to have a high torque and a small inertia, and the wheel effect has been made small, and the constant linear velocity has been attained by executing fine control of the linear velocity (CLV control) through comparison of a disk linear velocity detection signal obtained from the pickup with a reference signal, with the number of revolutions of the spindle motor changed, for example, 0.28% to 1.12% at the inside and 0.12% to 0.47% at the outside of the CD.
In such playback apparatus, however, since the number of revolutions of the spindle motor having a considerable amount of inertia is minutely changed, some acceleration is required, and this causes changes in the torque. Thereby, the entire system is swung and playback effects of the CD are lessened due to the resultant vibration. Further, there has been a problem that electric noises are frequently produced because of the use of a high-torque spindle motor.